In the state of the art, clocked, switching power supplies are primarily applied for producing protective low voltages (voltages lower than 50 V). For producing a plurality of galvanically isolated output voltages with smaller output power, for example, flyback converters are used. This involves, in such case, a direct voltage converter, which is used for the transmission of electrical energy between two direct voltage circuits, which have different voltages, and which can be galvanically isolated from one another. The principle underlying the flyback converter is that a small amount of energy is stored in the magnetic field of a coil—for example, the primary winding of a transformer—and this energy is thereafter transferred to the secondary, or consumption, side of the transformer. This cycle is passed through some thousand times per second, so that a virtually continuous energy flow arises.
Such circuits function excellently for input voltage ranges up to a ratio of 4:1; that is to say, in the case of a maximal voltage of 250 V AC, the lower limit lies at 62.5 V AC. For larger input voltage ratios, a number of compromises must be made with regard to efficiency and control behavior. Associated therewith is the fact that some components must be dimensioned for a considerably greater power level, and thus are more expensive.